We report high-sensitivity detection of 2,4,6-trinitrotoluene (TNT) by using laser photoacoustic spectroscopy where the laser radiation is obtained from a continuous-wave room temperature high-power quantum cascade laser in an external grating cavity geometry. The external grating cavity quantum cascade laser is continuously tunable over Ϸ400 nm around 7.3 m and produces a maximum continuouswave power of Ϸ200 mW. The IR spectroscopic signature of TNT is sufficiently different from that of nitroglycerine so that unambiguous detection of TNT without false positives from traces of nitroglycerine is possible. We also report the results of spectroscopy of acetylene in the 7.3-m region to demonstrate continuous tunability of the IR source.quantum cascade lasers ͉ high-power lasers ͉ continuous-wave operation ͉ room temperature operation ͉ TNT detection D etection of illegally transported explosives has become important since the global rise in terrorism subsequent to the events of September 11, 2001. Although not a choice of suicide bombers, 2,4,6-trinitrotoluene (TNT) is a potent explosive for which techniques for detection on a person's body or in one's baggage is considered important for assuring safety of airports and air travel. As with detection of other similar compounds, such as chemical warfare agents, any detection scheme that claims to detect these targets must exhibit acceptable receiver operational characteristic (ROC) that assures detection at very low levels without an unacceptable level of false alarms (1, 2). The molecular mass of TNT (C 7 H 5 N 3 O 6 ) is almost exactly identical to the molecular mass of nitroglycerine (C 3 H 5 N 3 O 9 ) even though the chemical compositions of the two molecules are very different (TNT, 227.131 Da vs. nitroglycerine, 227.0872 Da). The nearly same molecular masses often lead to problems for unambiguous detection of TNT using techniques that rely on measuring the molecular mass of the species. On the other hand, the differences in the chemical structure between TNT and nitroglycerine lead to noticeably different infrared (IR) absorption signatures (3), making it possible to distinguish between the two. However, the detection of TNT in vapor phase is hampered by its low vapor pressure of Ϸ2 ϫ 10 Ϫ4 torr at 25°C. In this work, we report on studies of detection of TNT by using room-temperature (RT) quantum cascade laser (QCL)-based photoacoustic spectroscopy (QCL-PAS). The high sensitivity afforded by laser-based photoacoustic spectroscopy (L-PAS) (4) shows that the vapor-phase detection of TNT at an ambient temperature of Ϸ25°C is possible.Previously, CO and CO 2 lasers have been used for photoacoustic (PA) spectroscopic detection (3, 5) of vapors of explosives. However, both of these laser sources are step tunable, and neither of the lasers is able to access the strong absorption features of TNT that lie in the 6.0-7.5 m region. Quantum cascade lasers (QCLs), with their continuous tunability, should be the right sources for the detection of TNT and other species that do...
We report high-throughput, nondispersive optical multiplexing of laser beams using a scanning galvanometer. We have utilized this technique for multispecies trace-gas detection using multiple quantum cascade laser photoacoustic spectroscopy. We demonstrate switching from one laser to another in less than 1 s, a performance level needed for a comprehensive multispecies sensor, and a high signal-to-noise ratio detection of five gaseous components, NH(3), NO(2), dimethyl methyl phosphonate (DMMP, a simulant for nerve agents), acetone, and ethylene glycol, in a room air gas mixture containing approximately 3 ppb of NH(3), approximately 8 ppb of NO(2), approximately 20 ppb of DMMP, approximately 30 ppb of acetone, and approximately 40 ppb of ethylene glycol.
Triacetone triperoxide (C(9)H(18)O(6), molecular mass of 222.24 g/mol) (TATP) is a powerful explosive that is easy to synthesize using commonly available household chemicals, acetone, and hydrogen peroxide 1 2. Because of the simplicity of its synthesis, TATP is often the explosive of choice for terrorists, including suicide bombers. For providing safety to the population, early detection of TATP and isolation of such individuals are essential. We report unambiguous, high-sensitivity detection of TATP and its precursor, acetone, using room-temperature quantum cascade laser photoacoustic spectroscopy (QCL-PAS). The available sensitivity is such that TATP, carried on a person (at a nominal body temperature of 37 degrees C), should be detectable at some distance. The combination of demonstrated detection of TATP and acetone should be ideal for screening at airports and other public places for providing increased public safety.
First measurements of biomedical imaging using quantum cascade lasers (QCL) are presented. We report spectroscopic imaging of serum proteins using QCLs as an example for monitoring surface biocontamination. We found that dry smears of human serum can be spectroscopically imaged, identified, and quantified with high sensitivity and specificity. The core parts of the imaging platform consist of optically multiplexing three QCLs and an uncooled microbolometer camera. We show imaging of human serum proteins at 6.1, 9.25, and 9.5 μm QCLs with high sensitivity and specificity. The sensitivity limit of 3 μg/cm² of the human serum spot was measured at an S/N=3.The specificity of human serum detection was measured at 99% probability at a threshold of 77 μg/cm². We anticipate our imaging technique to be a starting point for more sophisticated biomolecular diagnostic applications.
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